In a hydraulic control system typically a valve group is used having an inlet module connected to a pump (or another pressure source) and a tank reservoir and several service modules connected to particular work functions. For safety aspects it might be necessary to block the service modules from the pump supply line. Such a safety function can be realized by controlling a spool which is implemented in the inlet module to open or close a connection between the pump port of the inlet module and a common pressure line in the valve group which is connected to the pressure gallery of the inlet module.
Such a safety function should be monitored. This typically requires a position transducer equipment measuring the displacement of the spool.
Although such a position transducer allows to reliably obtain an information about the position of the spool, it requires additional elements which have to be accommodated in or at the housing.